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<pre><span class="sourceLineNo">001</span>/*<a name="line.1"></a>
<span class="sourceLineNo">002</span> * Copyright (C) 2012 The Guava Authors<a name="line.2"></a>
<span class="sourceLineNo">003</span> *<a name="line.3"></a>
<span class="sourceLineNo">004</span> * Licensed under the Apache License, Version 2.0 (the "License");<a name="line.4"></a>
<span class="sourceLineNo">005</span> * you may not use this file except in compliance with the License.<a name="line.5"></a>
<span class="sourceLineNo">006</span> * You may obtain a copy of the License at<a name="line.6"></a>
<span class="sourceLineNo">007</span> *<a name="line.7"></a>
<span class="sourceLineNo">008</span> * http://www.apache.org/licenses/LICENSE-2.0<a name="line.8"></a>
<span class="sourceLineNo">009</span> *<a name="line.9"></a>
<span class="sourceLineNo">010</span> * Unless required by applicable law or agreed to in writing, software<a name="line.10"></a>
<span class="sourceLineNo">011</span> * distributed under the License is distributed on an "AS IS" BASIS,<a name="line.11"></a>
<span class="sourceLineNo">012</span> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<a name="line.12"></a>
<span class="sourceLineNo">013</span> * See the License for the specific language governing permissions and<a name="line.13"></a>
<span class="sourceLineNo">014</span> * limitations under the License.<a name="line.14"></a>
<span class="sourceLineNo">015</span> */<a name="line.15"></a>
<span class="sourceLineNo">016</span><a name="line.16"></a>
<span class="sourceLineNo">017</span>package com.google.common.util.concurrent;<a name="line.17"></a>
<span class="sourceLineNo">018</span><a name="line.18"></a>
<span class="sourceLineNo">019</span>import com.google.common.annotations.Beta;<a name="line.19"></a>
<span class="sourceLineNo">020</span>import com.google.common.annotations.VisibleForTesting;<a name="line.20"></a>
<span class="sourceLineNo">021</span>import com.google.common.base.Preconditions;<a name="line.21"></a>
<span class="sourceLineNo">022</span>import com.google.common.base.Ticker;<a name="line.22"></a>
<span class="sourceLineNo">023</span><a name="line.23"></a>
<span class="sourceLineNo">024</span>import java.util.concurrent.TimeUnit;<a name="line.24"></a>
<span class="sourceLineNo">025</span><a name="line.25"></a>
<span class="sourceLineNo">026</span>import javax.annotation.concurrent.ThreadSafe;<a name="line.26"></a>
<span class="sourceLineNo">027</span><a name="line.27"></a>
<span class="sourceLineNo">028</span>/**<a name="line.28"></a>
<span class="sourceLineNo">029</span> * A rate limiter. Conceptually, a rate limiter distributes permits at a<a name="line.29"></a>
<span class="sourceLineNo">030</span> * configurable rate. Each {@link #acquire()} blocks if necessary until a permit is<a name="line.30"></a>
<span class="sourceLineNo">031</span> * available, and then takes it. Once acquired, permits need not be released.<a name="line.31"></a>
<span class="sourceLineNo">032</span> *<a name="line.32"></a>
<span class="sourceLineNo">033</span> * &lt;p&gt;Rate limiters are often used to restrict the rate at which some<a name="line.33"></a>
<span class="sourceLineNo">034</span> * physical or logical resource is accessed. This is in contrast to {@link<a name="line.34"></a>
<span class="sourceLineNo">035</span> * java.util.concurrent.Semaphore} which restricts the number of concurrent<a name="line.35"></a>
<span class="sourceLineNo">036</span> * accesses instead of the rate (note though that concurrency and rate are closely related,<a name="line.36"></a>
<span class="sourceLineNo">037</span> * e.g. see &lt;a href="http://en.wikipedia.org/wiki/Little's_law"&gt;Little's Law&lt;/a&gt;).<a name="line.37"></a>
<span class="sourceLineNo">038</span> *<a name="line.38"></a>
<span class="sourceLineNo">039</span> * &lt;p&gt;A {@code RateLimiter} is defined primarily by the rate at which permits<a name="line.39"></a>
<span class="sourceLineNo">040</span> * are issued. Absent additional configuration, permits will be distributed at a<a name="line.40"></a>
<span class="sourceLineNo">041</span> * fixed rate, defined in terms of permits per second. Permits will be distributed<a name="line.41"></a>
<span class="sourceLineNo">042</span> * smoothly, with the delay between individual permits being adjusted to ensure<a name="line.42"></a>
<span class="sourceLineNo">043</span> * that the configured rate is maintained.<a name="line.43"></a>
<span class="sourceLineNo">044</span> *<a name="line.44"></a>
<span class="sourceLineNo">045</span> * &lt;p&gt;It is possible to configure a {@code RateLimiter} to have a warmup<a name="line.45"></a>
<span class="sourceLineNo">046</span> * period during which time the permits issued each second steadily increases until<a name="line.46"></a>
<span class="sourceLineNo">047</span> * it hits the stable rate.<a name="line.47"></a>
<span class="sourceLineNo">048</span> *<a name="line.48"></a>
<span class="sourceLineNo">049</span> * &lt;p&gt;As an example, imagine that we have a list of tasks to execute, but we don't want to<a name="line.49"></a>
<span class="sourceLineNo">050</span> * submit more than 2 per second:<a name="line.50"></a>
<span class="sourceLineNo">051</span> *&lt;pre&gt;  {@code<a name="line.51"></a>
<span class="sourceLineNo">052</span> *  final RateLimiter rateLimiter = RateLimiter.create(2.0); // rate is "2 permits per second"<a name="line.52"></a>
<span class="sourceLineNo">053</span> *  void submitTasks(List&lt;Runnable&gt; tasks, Executor executor) {<a name="line.53"></a>
<span class="sourceLineNo">054</span> *    for (Runnable task : tasks) {<a name="line.54"></a>
<span class="sourceLineNo">055</span> *      rateLimiter.acquire(); // may wait<a name="line.55"></a>
<span class="sourceLineNo">056</span> *      executor.execute(task);<a name="line.56"></a>
<span class="sourceLineNo">057</span> *    }<a name="line.57"></a>
<span class="sourceLineNo">058</span> *  }<a name="line.58"></a>
<span class="sourceLineNo">059</span> *}&lt;/pre&gt;<a name="line.59"></a>
<span class="sourceLineNo">060</span> *<a name="line.60"></a>
<span class="sourceLineNo">061</span> * &lt;p&gt;As another example, imagine that we produce a stream of data, and we want to cap it<a name="line.61"></a>
<span class="sourceLineNo">062</span> * at 5kb per second. This could be accomplished by requiring a permit per byte, and specifying<a name="line.62"></a>
<span class="sourceLineNo">063</span> * a rate of 5000 permits per second:<a name="line.63"></a>
<span class="sourceLineNo">064</span> *&lt;pre&gt;  {@code<a name="line.64"></a>
<span class="sourceLineNo">065</span> *  final RateLimiter rateLimiter = RateLimiter.create(5000.0); // rate = 5000 permits per second<a name="line.65"></a>
<span class="sourceLineNo">066</span> *  void submitPacket(byte[] packet) {<a name="line.66"></a>
<span class="sourceLineNo">067</span> *    rateLimiter.acquire(packet.length);<a name="line.67"></a>
<span class="sourceLineNo">068</span> *    networkService.send(packet);<a name="line.68"></a>
<span class="sourceLineNo">069</span> *  }<a name="line.69"></a>
<span class="sourceLineNo">070</span> *}&lt;/pre&gt;<a name="line.70"></a>
<span class="sourceLineNo">071</span> *<a name="line.71"></a>
<span class="sourceLineNo">072</span> * &lt;p&gt;It is important to note that the number of permits requested &lt;i&gt;never&lt;/i&gt;<a name="line.72"></a>
<span class="sourceLineNo">073</span> * affect the throttling of the request itself (an invocation to {@code acquire(1)}<a name="line.73"></a>
<span class="sourceLineNo">074</span> * and an invocation to {@code acquire(1000)} will result in exactly the same throttling, if any),<a name="line.74"></a>
<span class="sourceLineNo">075</span> * but it affects the throttling of the &lt;i&gt;next&lt;/i&gt; request. I.e., if an expensive task<a name="line.75"></a>
<span class="sourceLineNo">076</span> * arrives at an idle RateLimiter, it will be granted immediately, but it is the &lt;i&gt;next&lt;/i&gt;<a name="line.76"></a>
<span class="sourceLineNo">077</span> * request that will experience extra throttling, thus paying for the cost of the expensive<a name="line.77"></a>
<span class="sourceLineNo">078</span> * task.<a name="line.78"></a>
<span class="sourceLineNo">079</span> *<a name="line.79"></a>
<span class="sourceLineNo">080</span> * &lt;p&gt;Note: {@code RateLimiter} does not provide fairness guarantees.<a name="line.80"></a>
<span class="sourceLineNo">081</span> *<a name="line.81"></a>
<span class="sourceLineNo">082</span> * @author Dimitris Andreou<a name="line.82"></a>
<span class="sourceLineNo">083</span> * @since 13.0<a name="line.83"></a>
<span class="sourceLineNo">084</span> */<a name="line.84"></a>
<span class="sourceLineNo">085</span>// TODO(user): switch to nano precision. A natural unit of cost is "bytes", and a micro precision<a name="line.85"></a>
<span class="sourceLineNo">086</span>//     would mean a maximum rate of "1MB/s", which might be small in some cases.<a name="line.86"></a>
<span class="sourceLineNo">087</span>@ThreadSafe<a name="line.87"></a>
<span class="sourceLineNo">088</span>@Beta<a name="line.88"></a>
<span class="sourceLineNo">089</span>public abstract class RateLimiter {<a name="line.89"></a>
<span class="sourceLineNo">090</span>  /*<a name="line.90"></a>
<span class="sourceLineNo">091</span>   * How is the RateLimiter designed, and why?<a name="line.91"></a>
<span class="sourceLineNo">092</span>   *<a name="line.92"></a>
<span class="sourceLineNo">093</span>   * The primary feature of a RateLimiter is its "stable rate", the maximum rate that<a name="line.93"></a>
<span class="sourceLineNo">094</span>   * is should allow at normal conditions. This is enforced by "throttling" incoming<a name="line.94"></a>
<span class="sourceLineNo">095</span>   * requests as needed, i.e. compute, for an incoming request, the appropriate throttle time,<a name="line.95"></a>
<span class="sourceLineNo">096</span>   * and make the calling thread wait as much.<a name="line.96"></a>
<span class="sourceLineNo">097</span>   *<a name="line.97"></a>
<span class="sourceLineNo">098</span>   * The simplest way to maintain a rate of QPS is to keep the timestamp of the last<a name="line.98"></a>
<span class="sourceLineNo">099</span>   * granted request, and ensure that (1/QPS) seconds have elapsed since then. For example,<a name="line.99"></a>
<span class="sourceLineNo">100</span>   * for a rate of QPS=5 (5 tokens per second), if we ensure that a request isn't granted<a name="line.100"></a>
<span class="sourceLineNo">101</span>   * earlier than 200ms after the the last one, then we achieve the intended rate.<a name="line.101"></a>
<span class="sourceLineNo">102</span>   * If a request comes and the last request was granted only 100ms ago, then we wait for<a name="line.102"></a>
<span class="sourceLineNo">103</span>   * another 100ms. At this rate, serving 15 fresh permits (i.e. for an acquire(15) request)<a name="line.103"></a>
<span class="sourceLineNo">104</span>   * naturally takes 3 seconds.<a name="line.104"></a>
<span class="sourceLineNo">105</span>   *<a name="line.105"></a>
<span class="sourceLineNo">106</span>   * It is important to realize that such a RateLimiter has a very superficial memory<a name="line.106"></a>
<span class="sourceLineNo">107</span>   * of the past: it only remembers the last request. What if the RateLimiter was unused for<a name="line.107"></a>
<span class="sourceLineNo">108</span>   * a long period of time, then a request arrived and was immediately granted?<a name="line.108"></a>
<span class="sourceLineNo">109</span>   * This RateLimiter would immediately forget about that past underutilization. This may<a name="line.109"></a>
<span class="sourceLineNo">110</span>   * result in either underutilization or overflow, depending on the real world consequences<a name="line.110"></a>
<span class="sourceLineNo">111</span>   * of not using the expected rate.<a name="line.111"></a>
<span class="sourceLineNo">112</span>   *<a name="line.112"></a>
<span class="sourceLineNo">113</span>   * Past underutilization could mean that excess resources are available. Then, the RateLimiter<a name="line.113"></a>
<span class="sourceLineNo">114</span>   * should speed up for a while, to take advantage of these resources. This is important<a name="line.114"></a>
<span class="sourceLineNo">115</span>   * when the rate is applied to networking (limiting bandwidth), where past underutilization<a name="line.115"></a>
<span class="sourceLineNo">116</span>   * typically translates to "almost empty buffers", which can be filled immediately.<a name="line.116"></a>
<span class="sourceLineNo">117</span>   *<a name="line.117"></a>
<span class="sourceLineNo">118</span>   * On the other hand, past underutilization could mean that "the server responsible for<a name="line.118"></a>
<span class="sourceLineNo">119</span>   * handling the request has become less ready for future requests", i.e. its caches become<a name="line.119"></a>
<span class="sourceLineNo">120</span>   * stale, and requests become more likely to trigger expensive operations (a more extreme<a name="line.120"></a>
<span class="sourceLineNo">121</span>   * case of this example is when a server has just booted, and it is mostly busy with getting<a name="line.121"></a>
<span class="sourceLineNo">122</span>   * itself up to speed).<a name="line.122"></a>
<span class="sourceLineNo">123</span>   *<a name="line.123"></a>
<span class="sourceLineNo">124</span>   * To deal with such scenarios, we add an extra dimension, that of "past underutilization",<a name="line.124"></a>
<span class="sourceLineNo">125</span>   * modeled by "storedPermits" variable. This variable is zero when there is no<a name="line.125"></a>
<span class="sourceLineNo">126</span>   * underutilization, and it can grow up to maxStoredPermits, for sufficiently large<a name="line.126"></a>
<span class="sourceLineNo">127</span>   * underutilization. So, the requested permits, by an invocation acquire(permits),<a name="line.127"></a>
<span class="sourceLineNo">128</span>   * are served from:<a name="line.128"></a>
<span class="sourceLineNo">129</span>   * - stored permits (if available)<a name="line.129"></a>
<span class="sourceLineNo">130</span>   * - fresh permits (for any remaining permits)<a name="line.130"></a>
<span class="sourceLineNo">131</span>   *<a name="line.131"></a>
<span class="sourceLineNo">132</span>   * How this works is best explained with an example:<a name="line.132"></a>
<span class="sourceLineNo">133</span>   *<a name="line.133"></a>
<span class="sourceLineNo">134</span>   * For a RateLimiter that produces 1 token per second, every second<a name="line.134"></a>
<span class="sourceLineNo">135</span>   * that goes by with the RateLimiter being unused, we increase storedPermits by 1.<a name="line.135"></a>
<span class="sourceLineNo">136</span>   * Say we leave the RateLimiter unused for 10 seconds (i.e., we expected a request at time<a name="line.136"></a>
<span class="sourceLineNo">137</span>   * X, but we are at time X + 10 seconds before a request actually arrives; this is<a name="line.137"></a>
<span class="sourceLineNo">138</span>   * also related to the point made in the last paragraph), thus storedPermits<a name="line.138"></a>
<span class="sourceLineNo">139</span>   * becomes 10.0 (assuming maxStoredPermits &gt;= 10.0). At that point, a request of acquire(3)<a name="line.139"></a>
<span class="sourceLineNo">140</span>   * arrives. We serve this request out of storedPermits, and reduce that to 7.0 (how this is<a name="line.140"></a>
<span class="sourceLineNo">141</span>   * translated to throttling time is discussed later). Immediately after, assume that an<a name="line.141"></a>
<span class="sourceLineNo">142</span>   * acquire(10) request arriving. We serve the request partly from storedPermits,<a name="line.142"></a>
<span class="sourceLineNo">143</span>   * using all the remaining 7.0 permits, and the remaining 3.0, we serve them by fresh permits<a name="line.143"></a>
<span class="sourceLineNo">144</span>   * produced by the rate limiter.<a name="line.144"></a>
<span class="sourceLineNo">145</span>   *<a name="line.145"></a>
<span class="sourceLineNo">146</span>   * We already know how much time it takes to serve 3 fresh permits: if the rate is<a name="line.146"></a>
<span class="sourceLineNo">147</span>   * "1 token per second", then this will take 3 seconds. But what does it mean to serve 7<a name="line.147"></a>
<span class="sourceLineNo">148</span>   * stored permits? As explained above, there is no unique answer. If we are primarily<a name="line.148"></a>
<span class="sourceLineNo">149</span>   * interested to deal with underutilization, then we want stored permits to be given out<a name="line.149"></a>
<span class="sourceLineNo">150</span>   * /faster/ than fresh ones, because underutilization = free resources for the taking.<a name="line.150"></a>
<span class="sourceLineNo">151</span>   * If we are primarily interested to deal with overflow, then stored permits could<a name="line.151"></a>
<span class="sourceLineNo">152</span>   * be given out /slower/ than fresh ones. Thus, we require a (different in each case)<a name="line.152"></a>
<span class="sourceLineNo">153</span>   * function that translates storedPermits to throtting time.<a name="line.153"></a>
<span class="sourceLineNo">154</span>   *<a name="line.154"></a>
<span class="sourceLineNo">155</span>   * This role is played by storedPermitsToWaitTime(double storedPermits, double permitsToTake).<a name="line.155"></a>
<span class="sourceLineNo">156</span>   * The underlying model is a continuous function mapping storedPermits<a name="line.156"></a>
<span class="sourceLineNo">157</span>   * (from 0.0 to maxStoredPermits) onto the 1/rate (i.e. intervals) that is effective at the given<a name="line.157"></a>
<span class="sourceLineNo">158</span>   * storedPermits. "storedPermits" essentially measure unused time; we spend unused time<a name="line.158"></a>
<span class="sourceLineNo">159</span>   * buying/storing permits. Rate is "permits / time", thus "1 / rate = time / permits".<a name="line.159"></a>
<span class="sourceLineNo">160</span>   * Thus, "1/rate" (time / permits) times "permits" gives time, i.e., integrals on this<a name="line.160"></a>
<span class="sourceLineNo">161</span>   * function (which is what storedPermitsToWaitTime() computes) correspond to minimum intervals<a name="line.161"></a>
<span class="sourceLineNo">162</span>   * between subsequent requests, for the specified number of requested permits.<a name="line.162"></a>
<span class="sourceLineNo">163</span>   *<a name="line.163"></a>
<span class="sourceLineNo">164</span>   * Here is an example of storedPermitsToWaitTime:<a name="line.164"></a>
<span class="sourceLineNo">165</span>   * If storedPermits == 10.0, and we want 3 permits, we take them from storedPermits,<a name="line.165"></a>
<span class="sourceLineNo">166</span>   * reducing them to 7.0, and compute the throttling for these as a call to<a name="line.166"></a>
<span class="sourceLineNo">167</span>   * storedPermitsToWaitTime(storedPermits = 10.0, permitsToTake = 3.0), which will<a name="line.167"></a>
<span class="sourceLineNo">168</span>   * evaluate the integral of the function from 7.0 to 10.0.<a name="line.168"></a>
<span class="sourceLineNo">169</span>   *<a name="line.169"></a>
<span class="sourceLineNo">170</span>   * Using integrals guarantees that the effect of a single acquire(3) is equivalent<a name="line.170"></a>
<span class="sourceLineNo">171</span>   * to { acquire(1); acquire(1); acquire(1); }, or { acquire(2); acquire(1); }, etc,<a name="line.171"></a>
<span class="sourceLineNo">172</span>   * since the integral of the function in [7.0, 10.0] is equivalent to the sum of the<a name="line.172"></a>
<span class="sourceLineNo">173</span>   * integrals of [7.0, 8.0], [8.0, 9.0], [9.0, 10.0] (and so on), no matter<a name="line.173"></a>
<span class="sourceLineNo">174</span>   * what the function is. This guarantees that we handle correctly requests of varying weight<a name="line.174"></a>
<span class="sourceLineNo">175</span>   * (permits), /no matter/ what the actual function is - so we can tweak the latter freely.<a name="line.175"></a>
<span class="sourceLineNo">176</span>   * (The only requirement, obviously, is that we can compute its integrals).<a name="line.176"></a>
<span class="sourceLineNo">177</span>   *<a name="line.177"></a>
<span class="sourceLineNo">178</span>   * Note well that if, for this function, we chose a horizontal line, at height of exactly<a name="line.178"></a>
<span class="sourceLineNo">179</span>   * (1/QPS), then the effect of the function is non-existent: we serve storedPermits at<a name="line.179"></a>
<span class="sourceLineNo">180</span>   * exactly the same cost as fresh ones (1/QPS is the cost for each). We use this trick later.<a name="line.180"></a>
<span class="sourceLineNo">181</span>   *<a name="line.181"></a>
<span class="sourceLineNo">182</span>   * If we pick a function that goes /below/ that horizontal line, it means that we reduce<a name="line.182"></a>
<span class="sourceLineNo">183</span>   * the area of the function, thus time. Thus, the RateLimiter becomes /faster/ after a<a name="line.183"></a>
<span class="sourceLineNo">184</span>   * period of underutilization. If, on the other hand, we pick a function that<a name="line.184"></a>
<span class="sourceLineNo">185</span>   * goes /above/ that horizontal line, then it means that the area (time) is increased,<a name="line.185"></a>
<span class="sourceLineNo">186</span>   * thus storedPermits are more costly than fresh permits, thus the RateLimiter becomes<a name="line.186"></a>
<span class="sourceLineNo">187</span>   * /slower/ after a period of underutilization.<a name="line.187"></a>
<span class="sourceLineNo">188</span>   *<a name="line.188"></a>
<span class="sourceLineNo">189</span>   * Last, but not least: consider a RateLimiter with rate of 1 permit per second, currently<a name="line.189"></a>
<span class="sourceLineNo">190</span>   * completely unused, and an expensive acquire(100) request comes. It would be nonsensical<a name="line.190"></a>
<span class="sourceLineNo">191</span>   * to just wait for 100 seconds, and /then/ start the actual task. Why wait without doing<a name="line.191"></a>
<span class="sourceLineNo">192</span>   * anything? A much better approach is to /allow/ the request right away (as if it was an<a name="line.192"></a>
<span class="sourceLineNo">193</span>   * acquire(1) request instead), and postpone /subsequent/ requests as needed. In this version,<a name="line.193"></a>
<span class="sourceLineNo">194</span>   * we allow starting the task immediately, and postpone by 100 seconds future requests,<a name="line.194"></a>
<span class="sourceLineNo">195</span>   * thus we allow for work to get done in the meantime instead of waiting idly.<a name="line.195"></a>
<span class="sourceLineNo">196</span>   *<a name="line.196"></a>
<span class="sourceLineNo">197</span>   * This has important consequences: it means that the RateLimiter doesn't remember the time<a name="line.197"></a>
<span class="sourceLineNo">198</span>   * of the _last_ request, but it remembers the (expected) time of the _next_ request. This<a name="line.198"></a>
<span class="sourceLineNo">199</span>   * also enables us to tell immediately (see tryAcquire(timeout)) whether a particular<a name="line.199"></a>
<span class="sourceLineNo">200</span>   * timeout is enough to get us to the point of the next scheduling time, since we always<a name="line.200"></a>
<span class="sourceLineNo">201</span>   * maintain that. And what we mean by "an unused RateLimiter" is also defined by that<a name="line.201"></a>
<span class="sourceLineNo">202</span>   * notion: when we observe that the "expected arrival time of the next request" is actually<a name="line.202"></a>
<span class="sourceLineNo">203</span>   * in the past, then the difference (now - past) is the amount of time that the RateLimiter<a name="line.203"></a>
<span class="sourceLineNo">204</span>   * was formally unused, and it is that amount of time which we translate to storedPermits.<a name="line.204"></a>
<span class="sourceLineNo">205</span>   * (We increase storedPermits with the amount of permits that would have been produced<a name="line.205"></a>
<span class="sourceLineNo">206</span>   * in that idle time). So, if rate == 1 permit per second, and arrivals come exactly<a name="line.206"></a>
<span class="sourceLineNo">207</span>   * one second after the previous, then storedPermits is _never_ increased -- we would only<a name="line.207"></a>
<span class="sourceLineNo">208</span>   * increase it for arrivals _later_ than the expected one second.<a name="line.208"></a>
<span class="sourceLineNo">209</span>   */<a name="line.209"></a>
<span class="sourceLineNo">210</span><a name="line.210"></a>
<span class="sourceLineNo">211</span>  /**<a name="line.211"></a>
<span class="sourceLineNo">212</span>   * Creates a {@code RateLimiter} with the specified stable throughput, given as<a name="line.212"></a>
<span class="sourceLineNo">213</span>   * "permits per second" (commonly referred to as &lt;i&gt;QPS&lt;/i&gt;, queries per second).<a name="line.213"></a>
<span class="sourceLineNo">214</span>   *<a name="line.214"></a>
<span class="sourceLineNo">215</span>   * &lt;p&gt;The returned {@code RateLimiter} ensures that on average no more than {@code<a name="line.215"></a>
<span class="sourceLineNo">216</span>   * permitsPerSecond} are issued during any given second, with sustained requests<a name="line.216"></a>
<span class="sourceLineNo">217</span>   * being smoothly spread over each second. When the incoming request rate exceeds<a name="line.217"></a>
<span class="sourceLineNo">218</span>   * {@code permitsPerSecond} the rate limiter will release one permit every {@code<a name="line.218"></a>
<span class="sourceLineNo">219</span>   * (1.0 / permitsPerSecond)} seconds. When the rate limiter is unused,<a name="line.219"></a>
<span class="sourceLineNo">220</span>   * bursts of up to {@code permitsPerSecond} permits will be allowed, with subsequent<a name="line.220"></a>
<span class="sourceLineNo">221</span>   * requests being smoothly limited at the stable rate of {@code permitsPerSecond}.<a name="line.221"></a>
<span class="sourceLineNo">222</span>   *<a name="line.222"></a>
<span class="sourceLineNo">223</span>   * @param permitsPerSecond the rate of the returned {@code RateLimiter}, measured in<a name="line.223"></a>
<span class="sourceLineNo">224</span>   *        how many permits become available per second.<a name="line.224"></a>
<span class="sourceLineNo">225</span>   */<a name="line.225"></a>
<span class="sourceLineNo">226</span>  public static RateLimiter create(double permitsPerSecond) {<a name="line.226"></a>
<span class="sourceLineNo">227</span>    return create(SleepingTicker.SYSTEM_TICKER, permitsPerSecond);<a name="line.227"></a>
<span class="sourceLineNo">228</span>  }<a name="line.228"></a>
<span class="sourceLineNo">229</span><a name="line.229"></a>
<span class="sourceLineNo">230</span>  @VisibleForTesting<a name="line.230"></a>
<span class="sourceLineNo">231</span>  static RateLimiter create(SleepingTicker ticker, double permitsPerSecond) {<a name="line.231"></a>
<span class="sourceLineNo">232</span>    RateLimiter rateLimiter = new Bursty(ticker);<a name="line.232"></a>
<span class="sourceLineNo">233</span>    rateLimiter.setRate(permitsPerSecond);<a name="line.233"></a>
<span class="sourceLineNo">234</span>    return rateLimiter;<a name="line.234"></a>
<span class="sourceLineNo">235</span>  }<a name="line.235"></a>
<span class="sourceLineNo">236</span><a name="line.236"></a>
<span class="sourceLineNo">237</span>  /**<a name="line.237"></a>
<span class="sourceLineNo">238</span>   * Creates a {@code RateLimiter} with the specified stable throughput, given as<a name="line.238"></a>
<span class="sourceLineNo">239</span>   * "permits per second" (commonly referred to as &lt;i&gt;QPS&lt;/i&gt;, queries per second), and a<a name="line.239"></a>
<span class="sourceLineNo">240</span>   * &lt;i&gt;warmup period&lt;/i&gt;, during which the {@code RateLimiter} smoothly ramps up its rate,<a name="line.240"></a>
<span class="sourceLineNo">241</span>   * until it reaches its maximum rate at the end of the period (as long as there are enough<a name="line.241"></a>
<span class="sourceLineNo">242</span>   * requests to saturate it). Similarly, if the {@code RateLimiter} is left &lt;i&gt;unused&lt;/i&gt; for<a name="line.242"></a>
<span class="sourceLineNo">243</span>   * a duration of {@code warmupPeriod}, it will gradually return to its "cold" state,<a name="line.243"></a>
<span class="sourceLineNo">244</span>   * i.e. it will go through the same warming up process as when it was first created.<a name="line.244"></a>
<span class="sourceLineNo">245</span>   *<a name="line.245"></a>
<span class="sourceLineNo">246</span>   * &lt;p&gt;The returned {@code RateLimiter} is intended for cases where the resource that actually<a name="line.246"></a>
<span class="sourceLineNo">247</span>   * fulfils the requests (e.g., a remote server) needs "warmup" time, rather than<a name="line.247"></a>
<span class="sourceLineNo">248</span>   * being immediately accessed at the stable (maximum) rate.<a name="line.248"></a>
<span class="sourceLineNo">249</span>   *<a name="line.249"></a>
<span class="sourceLineNo">250</span>   * &lt;p&gt;The returned {@code RateLimiter} starts in a "cold" state (i.e. the warmup period<a name="line.250"></a>
<span class="sourceLineNo">251</span>   * will follow), and if it is left unused for long enough, it will return to that state.<a name="line.251"></a>
<span class="sourceLineNo">252</span>   *<a name="line.252"></a>
<span class="sourceLineNo">253</span>   * @param permitsPerSecond the rate of the returned {@code RateLimiter}, measured in<a name="line.253"></a>
<span class="sourceLineNo">254</span>   *        how many permits become available per second<a name="line.254"></a>
<span class="sourceLineNo">255</span>   * @param warmupPeriod the duration of the period where the {@code RateLimiter} ramps up its<a name="line.255"></a>
<span class="sourceLineNo">256</span>   *        rate, before reaching its stable (maximum) rate<a name="line.256"></a>
<span class="sourceLineNo">257</span>   * @param unit the time unit of the warmupPeriod argument<a name="line.257"></a>
<span class="sourceLineNo">258</span>   */<a name="line.258"></a>
<span class="sourceLineNo">259</span>  // TODO(user): add a burst size of 1-second-worth of permits, as in the metronome?<a name="line.259"></a>
<span class="sourceLineNo">260</span>  public static RateLimiter create(double permitsPerSecond, long warmupPeriod, TimeUnit unit) {<a name="line.260"></a>
<span class="sourceLineNo">261</span>    return create(SleepingTicker.SYSTEM_TICKER, permitsPerSecond, warmupPeriod, unit);<a name="line.261"></a>
<span class="sourceLineNo">262</span>  }<a name="line.262"></a>
<span class="sourceLineNo">263</span><a name="line.263"></a>
<span class="sourceLineNo">264</span>  @VisibleForTesting<a name="line.264"></a>
<span class="sourceLineNo">265</span>  static RateLimiter create(<a name="line.265"></a>
<span class="sourceLineNo">266</span>      SleepingTicker ticker, double permitsPerSecond, long warmupPeriod, TimeUnit timeUnit) {<a name="line.266"></a>
<span class="sourceLineNo">267</span>    RateLimiter rateLimiter = new WarmingUp(ticker, warmupPeriod, timeUnit);<a name="line.267"></a>
<span class="sourceLineNo">268</span>    rateLimiter.setRate(permitsPerSecond);<a name="line.268"></a>
<span class="sourceLineNo">269</span>    return rateLimiter;<a name="line.269"></a>
<span class="sourceLineNo">270</span>  }<a name="line.270"></a>
<span class="sourceLineNo">271</span><a name="line.271"></a>
<span class="sourceLineNo">272</span>  @VisibleForTesting<a name="line.272"></a>
<span class="sourceLineNo">273</span>  static RateLimiter createBursty(<a name="line.273"></a>
<span class="sourceLineNo">274</span>      SleepingTicker ticker, double permitsPerSecond, int maxBurstSize) {<a name="line.274"></a>
<span class="sourceLineNo">275</span>    Bursty rateLimiter = new Bursty(ticker);<a name="line.275"></a>
<span class="sourceLineNo">276</span>    rateLimiter.setRate(permitsPerSecond);<a name="line.276"></a>
<span class="sourceLineNo">277</span>    rateLimiter.maxPermits = maxBurstSize;<a name="line.277"></a>
<span class="sourceLineNo">278</span>    return rateLimiter;<a name="line.278"></a>
<span class="sourceLineNo">279</span>  }<a name="line.279"></a>
<span class="sourceLineNo">280</span><a name="line.280"></a>
<span class="sourceLineNo">281</span>  /**<a name="line.281"></a>
<span class="sourceLineNo">282</span>   * The underlying timer; used both to measure elapsed time and sleep as necessary. A separate<a name="line.282"></a>
<span class="sourceLineNo">283</span>   * object to facilitate testing.<a name="line.283"></a>
<span class="sourceLineNo">284</span>   */<a name="line.284"></a>
<span class="sourceLineNo">285</span>  private final SleepingTicker ticker;<a name="line.285"></a>
<span class="sourceLineNo">286</span><a name="line.286"></a>
<span class="sourceLineNo">287</span>  /**<a name="line.287"></a>
<span class="sourceLineNo">288</span>   * The timestamp when the RateLimiter was created; used to avoid possible overflow/time-wrapping<a name="line.288"></a>
<span class="sourceLineNo">289</span>   * errors.<a name="line.289"></a>
<span class="sourceLineNo">290</span>   */<a name="line.290"></a>
<span class="sourceLineNo">291</span>  private final long offsetNanos;<a name="line.291"></a>
<span class="sourceLineNo">292</span><a name="line.292"></a>
<span class="sourceLineNo">293</span>  /**<a name="line.293"></a>
<span class="sourceLineNo">294</span>   * The currently stored permits.<a name="line.294"></a>
<span class="sourceLineNo">295</span>   */<a name="line.295"></a>
<span class="sourceLineNo">296</span>  double storedPermits;<a name="line.296"></a>
<span class="sourceLineNo">297</span><a name="line.297"></a>
<span class="sourceLineNo">298</span>  /**<a name="line.298"></a>
<span class="sourceLineNo">299</span>   * The maximum number of stored permits.<a name="line.299"></a>
<span class="sourceLineNo">300</span>   */<a name="line.300"></a>
<span class="sourceLineNo">301</span>  double maxPermits;<a name="line.301"></a>
<span class="sourceLineNo">302</span><a name="line.302"></a>
<span class="sourceLineNo">303</span>  /**<a name="line.303"></a>
<span class="sourceLineNo">304</span>   * The interval between two unit requests, at our stable rate. E.g., a stable rate of 5 permits<a name="line.304"></a>
<span class="sourceLineNo">305</span>   * per second has a stable interval of 200ms.<a name="line.305"></a>
<span class="sourceLineNo">306</span>   */<a name="line.306"></a>
<span class="sourceLineNo">307</span>  double stableIntervalMicros;<a name="line.307"></a>
<span class="sourceLineNo">308</span><a name="line.308"></a>
<span class="sourceLineNo">309</span>  /**<a name="line.309"></a>
<span class="sourceLineNo">310</span>   * The time when the next request (no matter its size) will be granted. After granting a request,<a name="line.310"></a>
<span class="sourceLineNo">311</span>   * this is pushed further in the future. Large requests push this further than small requests.<a name="line.311"></a>
<span class="sourceLineNo">312</span>   */<a name="line.312"></a>
<span class="sourceLineNo">313</span>  private long nextFreeTicketMicros = 0L; // could be either in the past or future<a name="line.313"></a>
<span class="sourceLineNo">314</span><a name="line.314"></a>
<span class="sourceLineNo">315</span>  private RateLimiter(SleepingTicker ticker) {<a name="line.315"></a>
<span class="sourceLineNo">316</span>    this.ticker = ticker;<a name="line.316"></a>
<span class="sourceLineNo">317</span>    this.offsetNanos = ticker.read();<a name="line.317"></a>
<span class="sourceLineNo">318</span>  }<a name="line.318"></a>
<span class="sourceLineNo">319</span><a name="line.319"></a>
<span class="sourceLineNo">320</span>  /**<a name="line.320"></a>
<span class="sourceLineNo">321</span>   * Updates the stable rate of this {@code RateLimiter}, that is, the<a name="line.321"></a>
<span class="sourceLineNo">322</span>   * {@code permitsPerSecond} argument provided in the factory method that<a name="line.322"></a>
<span class="sourceLineNo">323</span>   * constructed the {@code RateLimiter}. Currently throttled threads will &lt;b&gt;not&lt;/b&gt;<a name="line.323"></a>
<span class="sourceLineNo">324</span>   * be awakened as a result of this invocation, thus they do not observe the new rate;<a name="line.324"></a>
<span class="sourceLineNo">325</span>   * only subsequent requests will.<a name="line.325"></a>
<span class="sourceLineNo">326</span>   *<a name="line.326"></a>
<span class="sourceLineNo">327</span>   * &lt;p&gt;Note though that, since each request repays (by waiting, if necessary) the cost<a name="line.327"></a>
<span class="sourceLineNo">328</span>   * of the &lt;i&gt;previous&lt;/i&gt; request, this means that the very next request<a name="line.328"></a>
<span class="sourceLineNo">329</span>   * after an invocation to {@code setRate} will not be affected by the new rate;<a name="line.329"></a>
<span class="sourceLineNo">330</span>   * it will pay the cost of the previous request, which is in terms of the previous rate.<a name="line.330"></a>
<span class="sourceLineNo">331</span>   *<a name="line.331"></a>
<span class="sourceLineNo">332</span>   * &lt;p&gt;The behavior of the {@code RateLimiter} is not modified in any other way,<a name="line.332"></a>
<span class="sourceLineNo">333</span>   * e.g. if the {@code RateLimiter} was configured with a warmup period of 20 seconds,<a name="line.333"></a>
<span class="sourceLineNo">334</span>   * it still has a warmup period of 20 seconds after this method invocation.<a name="line.334"></a>
<span class="sourceLineNo">335</span>   *<a name="line.335"></a>
<span class="sourceLineNo">336</span>   * @param permitsPerSecond the new stable rate of this {@code RateLimiter}.<a name="line.336"></a>
<span class="sourceLineNo">337</span>   */<a name="line.337"></a>
<span class="sourceLineNo">338</span>  public final synchronized void setRate(double permitsPerSecond) {<a name="line.338"></a>
<span class="sourceLineNo">339</span>    Preconditions.checkArgument(permitsPerSecond &gt; 0.0<a name="line.339"></a>
<span class="sourceLineNo">340</span>        &amp;&amp; !Double.isNaN(permitsPerSecond), "rate must be positive");<a name="line.340"></a>
<span class="sourceLineNo">341</span>    resync(readSafeMicros());<a name="line.341"></a>
<span class="sourceLineNo">342</span>    double stableIntervalMicros = TimeUnit.SECONDS.toMicros(1L) / permitsPerSecond;<a name="line.342"></a>
<span class="sourceLineNo">343</span>    this.stableIntervalMicros =  stableIntervalMicros;<a name="line.343"></a>
<span class="sourceLineNo">344</span>    doSetRate(permitsPerSecond, stableIntervalMicros);<a name="line.344"></a>
<span class="sourceLineNo">345</span>  }<a name="line.345"></a>
<span class="sourceLineNo">346</span><a name="line.346"></a>
<span class="sourceLineNo">347</span>  abstract void doSetRate(double permitsPerSecond, double stableIntervalMicros);<a name="line.347"></a>
<span class="sourceLineNo">348</span><a name="line.348"></a>
<span class="sourceLineNo">349</span>  /**<a name="line.349"></a>
<span class="sourceLineNo">350</span>   * Returns the stable rate (as {@code permits per seconds}) with which this<a name="line.350"></a>
<span class="sourceLineNo">351</span>   * {@code RateLimiter} is configured with. The initial value of this is the same as<a name="line.351"></a>
<span class="sourceLineNo">352</span>   * the {@code permitsPerSecond} argument passed in the factory method that produced<a name="line.352"></a>
<span class="sourceLineNo">353</span>   * this {@code RateLimiter}, and it is only updated after invocations<a name="line.353"></a>
<span class="sourceLineNo">354</span>   * to {@linkplain #setRate}.<a name="line.354"></a>
<span class="sourceLineNo">355</span>   */<a name="line.355"></a>
<span class="sourceLineNo">356</span>  public final synchronized double getRate() {<a name="line.356"></a>
<span class="sourceLineNo">357</span>    return TimeUnit.SECONDS.toMicros(1L) / stableIntervalMicros;<a name="line.357"></a>
<span class="sourceLineNo">358</span>  }<a name="line.358"></a>
<span class="sourceLineNo">359</span><a name="line.359"></a>
<span class="sourceLineNo">360</span>  /**<a name="line.360"></a>
<span class="sourceLineNo">361</span>   * Acquires a permit from this {@code RateLimiter}, blocking until the request can be granted.<a name="line.361"></a>
<span class="sourceLineNo">362</span>   *<a name="line.362"></a>
<span class="sourceLineNo">363</span>   * &lt;p&gt;This method is equivalent to {@code acquire(1)}.<a name="line.363"></a>
<span class="sourceLineNo">364</span>   */<a name="line.364"></a>
<span class="sourceLineNo">365</span>  public void acquire() {<a name="line.365"></a>
<span class="sourceLineNo">366</span>    acquire(1);<a name="line.366"></a>
<span class="sourceLineNo">367</span>  }<a name="line.367"></a>
<span class="sourceLineNo">368</span><a name="line.368"></a>
<span class="sourceLineNo">369</span>  /**<a name="line.369"></a>
<span class="sourceLineNo">370</span>   * Acquires the given number of permits from this {@code RateLimiter}, blocking until the<a name="line.370"></a>
<span class="sourceLineNo">371</span>   * request be granted.<a name="line.371"></a>
<span class="sourceLineNo">372</span>   *<a name="line.372"></a>
<span class="sourceLineNo">373</span>   * @param permits the number of permits to acquire<a name="line.373"></a>
<span class="sourceLineNo">374</span>   */<a name="line.374"></a>
<span class="sourceLineNo">375</span>  public void acquire(int permits) {<a name="line.375"></a>
<span class="sourceLineNo">376</span>    checkPermits(permits);<a name="line.376"></a>
<span class="sourceLineNo">377</span>    long microsToWait;<a name="line.377"></a>
<span class="sourceLineNo">378</span>    synchronized (this) {<a name="line.378"></a>
<span class="sourceLineNo">379</span>      microsToWait = reserveNextTicket(permits, readSafeMicros());<a name="line.379"></a>
<span class="sourceLineNo">380</span>    }<a name="line.380"></a>
<span class="sourceLineNo">381</span>    ticker.sleepMicrosUninterruptibly(microsToWait);<a name="line.381"></a>
<span class="sourceLineNo">382</span>  }<a name="line.382"></a>
<span class="sourceLineNo">383</span><a name="line.383"></a>
<span class="sourceLineNo">384</span>  /**<a name="line.384"></a>
<span class="sourceLineNo">385</span>   * Acquires a permit from this {@code RateLimiter} if it can be obtained<a name="line.385"></a>
<span class="sourceLineNo">386</span>   * without exceeding the specified {@code timeout}, or returns {@code false}<a name="line.386"></a>
<span class="sourceLineNo">387</span>   * immediately (without waiting) if the permit would not have been granted<a name="line.387"></a>
<span class="sourceLineNo">388</span>   * before the timeout expired.<a name="line.388"></a>
<span class="sourceLineNo">389</span>   *<a name="line.389"></a>
<span class="sourceLineNo">390</span>   * &lt;p&gt;This method is equivalent to {@code tryAcquire(1, timeout, unit)}.<a name="line.390"></a>
<span class="sourceLineNo">391</span>   *<a name="line.391"></a>
<span class="sourceLineNo">392</span>   * @param timeout the maximum time to wait for the permit<a name="line.392"></a>
<span class="sourceLineNo">393</span>   * @param unit the time unit of the timeout argument<a name="line.393"></a>
<span class="sourceLineNo">394</span>   * @return {@code true} if the permit was acquired, {@code false} otherwise<a name="line.394"></a>
<span class="sourceLineNo">395</span>   */<a name="line.395"></a>
<span class="sourceLineNo">396</span>  public boolean tryAcquire(long timeout, TimeUnit unit) {<a name="line.396"></a>
<span class="sourceLineNo">397</span>    return tryAcquire(1, timeout, unit);<a name="line.397"></a>
<span class="sourceLineNo">398</span>  }<a name="line.398"></a>
<span class="sourceLineNo">399</span><a name="line.399"></a>
<span class="sourceLineNo">400</span>  /**<a name="line.400"></a>
<span class="sourceLineNo">401</span>   * Acquires permits from this {@link RateLimiter} if it can be acquired immediately without delay.<a name="line.401"></a>
<span class="sourceLineNo">402</span>   *<a name="line.402"></a>
<span class="sourceLineNo">403</span>   * &lt;p&gt;<a name="line.403"></a>
<span class="sourceLineNo">404</span>   * This method is equivalent to {@code tryAcquire(permits, 0, anyUnit)}.<a name="line.404"></a>
<span class="sourceLineNo">405</span>   *<a name="line.405"></a>
<span class="sourceLineNo">406</span>   * @param permits the number of permits to acquire<a name="line.406"></a>
<span class="sourceLineNo">407</span>   * @return {@code true} if the permits were acquired, {@code false} otherwise<a name="line.407"></a>
<span class="sourceLineNo">408</span>   * @since 14.0<a name="line.408"></a>
<span class="sourceLineNo">409</span>   */<a name="line.409"></a>
<span class="sourceLineNo">410</span>  public boolean tryAcquire(int permits) {<a name="line.410"></a>
<span class="sourceLineNo">411</span>    return tryAcquire(permits, 0, TimeUnit.MICROSECONDS);<a name="line.411"></a>
<span class="sourceLineNo">412</span>  }<a name="line.412"></a>
<span class="sourceLineNo">413</span><a name="line.413"></a>
<span class="sourceLineNo">414</span>  /**<a name="line.414"></a>
<span class="sourceLineNo">415</span>   * Acquires a permit from this {@link RateLimiter} if it can be acquired immediately without<a name="line.415"></a>
<span class="sourceLineNo">416</span>   * delay.<a name="line.416"></a>
<span class="sourceLineNo">417</span>   *<a name="line.417"></a>
<span class="sourceLineNo">418</span>   * &lt;p&gt;<a name="line.418"></a>
<span class="sourceLineNo">419</span>   * This method is equivalent to {@code tryAcquire(1)}.<a name="line.419"></a>
<span class="sourceLineNo">420</span>   *<a name="line.420"></a>
<span class="sourceLineNo">421</span>   * @return {@code true} if the permit was acquired, {@code false} otherwise<a name="line.421"></a>
<span class="sourceLineNo">422</span>   * @since 14.0<a name="line.422"></a>
<span class="sourceLineNo">423</span>   */<a name="line.423"></a>
<span class="sourceLineNo">424</span>  public boolean tryAcquire() {<a name="line.424"></a>
<span class="sourceLineNo">425</span>    return tryAcquire(1, 0, TimeUnit.MICROSECONDS);<a name="line.425"></a>
<span class="sourceLineNo">426</span>  }<a name="line.426"></a>
<span class="sourceLineNo">427</span><a name="line.427"></a>
<span class="sourceLineNo">428</span>  /**<a name="line.428"></a>
<span class="sourceLineNo">429</span>   * Acquires the given number of permits from this {@code RateLimiter} if it can be obtained<a name="line.429"></a>
<span class="sourceLineNo">430</span>   * without exceeding the specified {@code timeout}, or returns {@code false}<a name="line.430"></a>
<span class="sourceLineNo">431</span>   * immediately (without waiting) if the permits would not have been granted<a name="line.431"></a>
<span class="sourceLineNo">432</span>   * before the timeout expired.<a name="line.432"></a>
<span class="sourceLineNo">433</span>   *<a name="line.433"></a>
<span class="sourceLineNo">434</span>   * @param permits the number of permits to acquire<a name="line.434"></a>
<span class="sourceLineNo">435</span>   * @param timeout the maximum time to wait for the permits<a name="line.435"></a>
<span class="sourceLineNo">436</span>   * @param unit the time unit of the timeout argument<a name="line.436"></a>
<span class="sourceLineNo">437</span>   * @return {@code true} if the permits were acquired, {@code false} otherwise<a name="line.437"></a>
<span class="sourceLineNo">438</span>   */<a name="line.438"></a>
<span class="sourceLineNo">439</span>  public boolean tryAcquire(int permits, long timeout, TimeUnit unit) {<a name="line.439"></a>
<span class="sourceLineNo">440</span>    long timeoutMicros = unit.toMicros(timeout);<a name="line.440"></a>
<span class="sourceLineNo">441</span>    checkPermits(permits);<a name="line.441"></a>
<span class="sourceLineNo">442</span>    long microsToWait;<a name="line.442"></a>
<span class="sourceLineNo">443</span>    synchronized (this) {<a name="line.443"></a>
<span class="sourceLineNo">444</span>      long nowMicros = readSafeMicros();<a name="line.444"></a>
<span class="sourceLineNo">445</span>      if (nextFreeTicketMicros &gt; nowMicros + timeoutMicros) {<a name="line.445"></a>
<span class="sourceLineNo">446</span>        return false;<a name="line.446"></a>
<span class="sourceLineNo">447</span>      } else {<a name="line.447"></a>
<span class="sourceLineNo">448</span>        microsToWait = reserveNextTicket(permits, nowMicros);<a name="line.448"></a>
<span class="sourceLineNo">449</span>      }<a name="line.449"></a>
<span class="sourceLineNo">450</span>    }<a name="line.450"></a>
<span class="sourceLineNo">451</span>    ticker.sleepMicrosUninterruptibly(microsToWait);<a name="line.451"></a>
<span class="sourceLineNo">452</span>    return true;<a name="line.452"></a>
<span class="sourceLineNo">453</span>  }<a name="line.453"></a>
<span class="sourceLineNo">454</span><a name="line.454"></a>
<span class="sourceLineNo">455</span>  private static void checkPermits(int permits) {<a name="line.455"></a>
<span class="sourceLineNo">456</span>    Preconditions.checkArgument(permits &gt; 0, "Requested permits must be positive");<a name="line.456"></a>
<span class="sourceLineNo">457</span>  }<a name="line.457"></a>
<span class="sourceLineNo">458</span><a name="line.458"></a>
<span class="sourceLineNo">459</span>  /**<a name="line.459"></a>
<span class="sourceLineNo">460</span>   * Reserves next ticket and returns the wait time that the caller must wait for.<a name="line.460"></a>
<span class="sourceLineNo">461</span>   */<a name="line.461"></a>
<span class="sourceLineNo">462</span>  private long reserveNextTicket(double requiredPermits, long nowMicros) {<a name="line.462"></a>
<span class="sourceLineNo">463</span>    resync(nowMicros);<a name="line.463"></a>
<span class="sourceLineNo">464</span>    long microsToNextFreeTicket = nextFreeTicketMicros - nowMicros;<a name="line.464"></a>
<span class="sourceLineNo">465</span>    double storedPermitsToSpend = Math.min(requiredPermits, this.storedPermits);<a name="line.465"></a>
<span class="sourceLineNo">466</span>    double freshPermits = requiredPermits - storedPermitsToSpend;<a name="line.466"></a>
<span class="sourceLineNo">467</span><a name="line.467"></a>
<span class="sourceLineNo">468</span>    long waitMicros = storedPermitsToWaitTime(this.storedPermits, storedPermitsToSpend)<a name="line.468"></a>
<span class="sourceLineNo">469</span>        + (long) (freshPermits * stableIntervalMicros);<a name="line.469"></a>
<span class="sourceLineNo">470</span><a name="line.470"></a>
<span class="sourceLineNo">471</span>    this.nextFreeTicketMicros = nextFreeTicketMicros + waitMicros;<a name="line.471"></a>
<span class="sourceLineNo">472</span>    this.storedPermits -= storedPermitsToSpend;<a name="line.472"></a>
<span class="sourceLineNo">473</span>    return microsToNextFreeTicket;<a name="line.473"></a>
<span class="sourceLineNo">474</span>  }<a name="line.474"></a>
<span class="sourceLineNo">475</span><a name="line.475"></a>
<span class="sourceLineNo">476</span>  /**<a name="line.476"></a>
<span class="sourceLineNo">477</span>   * Translates a specified portion of our currently stored permits which we want to<a name="line.477"></a>
<span class="sourceLineNo">478</span>   * spend/acquire, into a throttling time. Conceptually, this evaluates the integral<a name="line.478"></a>
<span class="sourceLineNo">479</span>   * of the underlying function we use, for the range of<a name="line.479"></a>
<span class="sourceLineNo">480</span>   * [(storedPermits - permitsToTake), storedPermits].<a name="line.480"></a>
<span class="sourceLineNo">481</span>   *<a name="line.481"></a>
<span class="sourceLineNo">482</span>   * This always holds: {@code 0 &lt;= permitsToTake &lt;= storedPermits}<a name="line.482"></a>
<span class="sourceLineNo">483</span>   */<a name="line.483"></a>
<span class="sourceLineNo">484</span>  abstract long storedPermitsToWaitTime(double storedPermits, double permitsToTake);<a name="line.484"></a>
<span class="sourceLineNo">485</span><a name="line.485"></a>
<span class="sourceLineNo">486</span>  private void resync(long nowMicros) {<a name="line.486"></a>
<span class="sourceLineNo">487</span>    // if nextFreeTicket is in the past, resync to now<a name="line.487"></a>
<span class="sourceLineNo">488</span>    if (nowMicros &gt; nextFreeTicketMicros) {<a name="line.488"></a>
<span class="sourceLineNo">489</span>      storedPermits = Math.min(maxPermits,<a name="line.489"></a>
<span class="sourceLineNo">490</span>          storedPermits + (nowMicros - nextFreeTicketMicros) / stableIntervalMicros);<a name="line.490"></a>
<span class="sourceLineNo">491</span>      nextFreeTicketMicros = nowMicros;<a name="line.491"></a>
<span class="sourceLineNo">492</span>    }<a name="line.492"></a>
<span class="sourceLineNo">493</span>  }<a name="line.493"></a>
<span class="sourceLineNo">494</span><a name="line.494"></a>
<span class="sourceLineNo">495</span>  private long readSafeMicros() {<a name="line.495"></a>
<span class="sourceLineNo">496</span>    return TimeUnit.NANOSECONDS.toMicros(ticker.read() - offsetNanos);<a name="line.496"></a>
<span class="sourceLineNo">497</span>  }<a name="line.497"></a>
<span class="sourceLineNo">498</span><a name="line.498"></a>
<span class="sourceLineNo">499</span>  @Override<a name="line.499"></a>
<span class="sourceLineNo">500</span>  public String toString() {<a name="line.500"></a>
<span class="sourceLineNo">501</span>    return String.format("RateLimiter[stableRate=%3.1fqps]", 1000000.0 / stableIntervalMicros);<a name="line.501"></a>
<span class="sourceLineNo">502</span>  }<a name="line.502"></a>
<span class="sourceLineNo">503</span><a name="line.503"></a>
<span class="sourceLineNo">504</span>  /**<a name="line.504"></a>
<span class="sourceLineNo">505</span>   * This implements the following function:<a name="line.505"></a>
<span class="sourceLineNo">506</span>   *<a name="line.506"></a>
<span class="sourceLineNo">507</span>   *          ^ throttling<a name="line.507"></a>
<span class="sourceLineNo">508</span>   *          |<a name="line.508"></a>
<span class="sourceLineNo">509</span>   * 3*stable +                  /<a name="line.509"></a>
<span class="sourceLineNo">510</span>   * interval |                 /.<a name="line.510"></a>
<span class="sourceLineNo">511</span>   *  (cold)  |                / .<a name="line.511"></a>
<span class="sourceLineNo">512</span>   *          |               /  .   &lt;-- "warmup period" is the area of the trapezoid between<a name="line.512"></a>
<span class="sourceLineNo">513</span>   * 2*stable +              /   .       halfPermits and maxPermits<a name="line.513"></a>
<span class="sourceLineNo">514</span>   * interval |             /    .<a name="line.514"></a>
<span class="sourceLineNo">515</span>   *          |            /     .<a name="line.515"></a>
<span class="sourceLineNo">516</span>   *          |           /      .<a name="line.516"></a>
<span class="sourceLineNo">517</span>   *   stable +----------/  WARM . }<a name="line.517"></a>
<span class="sourceLineNo">518</span>   * interval |          .   UP  . } &lt;-- this rectangle (from 0 to maxPermits, and<a name="line.518"></a>
<span class="sourceLineNo">519</span>   *          |          . PERIOD. }     height == stableInterval) defines the cooldown period,<a name="line.519"></a>
<span class="sourceLineNo">520</span>   *          |          .       . }     and we want cooldownPeriod == warmupPeriod<a name="line.520"></a>
<span class="sourceLineNo">521</span>   *          |---------------------------------&gt; storedPermits<a name="line.521"></a>
<span class="sourceLineNo">522</span>   *              (halfPermits) (maxPermits)<a name="line.522"></a>
<span class="sourceLineNo">523</span>   *<a name="line.523"></a>
<span class="sourceLineNo">524</span>   * Before going into the details of this particular function, let's keep in mind the basics:<a name="line.524"></a>
<span class="sourceLineNo">525</span>   * 1) The state of the RateLimiter (storedPermits) is a vertical line in this figure.<a name="line.525"></a>
<span class="sourceLineNo">526</span>   * 2) When the RateLimiter is not used, this goes right (up to maxPermits)<a name="line.526"></a>
<span class="sourceLineNo">527</span>   * 3) When the RateLimiter is used, this goes left (down to zero), since if we have storedPermits,<a name="line.527"></a>
<span class="sourceLineNo">528</span>   *    we serve from those first<a name="line.528"></a>
<span class="sourceLineNo">529</span>   * 4) When _unused_, we go right at the same speed (rate)! I.e., if our rate is<a name="line.529"></a>
<span class="sourceLineNo">530</span>   *    2 permits per second, and 3 unused seconds pass, we will always save 6 permits<a name="line.530"></a>
<span class="sourceLineNo">531</span>   *    (no matter what our initial position was), up to maxPermits.<a name="line.531"></a>
<span class="sourceLineNo">532</span>   *    If we invert the rate, we get the "stableInterval" (interval between two requests<a name="line.532"></a>
<span class="sourceLineNo">533</span>   *    in a perfectly spaced out sequence of requests of the given rate). Thus, if you<a name="line.533"></a>
<span class="sourceLineNo">534</span>   *    want to see "how much time it will take to go from X storedPermits to X+K storedPermits?",<a name="line.534"></a>
<span class="sourceLineNo">535</span>   *    the answer is always stableInterval * K. In the same example, for 2 permits per second,<a name="line.535"></a>
<span class="sourceLineNo">536</span>   *    stableInterval is 500ms. Thus to go from X storedPermits to X+6 storedPermits, we<a name="line.536"></a>
<span class="sourceLineNo">537</span>   *    require 6 * 500ms = 3 seconds.<a name="line.537"></a>
<span class="sourceLineNo">538</span>   *<a name="line.538"></a>
<span class="sourceLineNo">539</span>   *    In short, the time it takes to move to the right (save K permits) is equal to the<a name="line.539"></a>
<span class="sourceLineNo">540</span>   *    rectangle of width == K and height == stableInterval.<a name="line.540"></a>
<span class="sourceLineNo">541</span>   * 4) When _used_, the time it takes, as explained in the introductory class note, is<a name="line.541"></a>
<span class="sourceLineNo">542</span>   *    equal to the integral of our function, between X permits and X-K permits, assuming<a name="line.542"></a>
<span class="sourceLineNo">543</span>   *    we want to spend K saved permits.<a name="line.543"></a>
<span class="sourceLineNo">544</span>   *<a name="line.544"></a>
<span class="sourceLineNo">545</span>   *    In summary, the time it takes to move to the left (spend K permits), is equal to the<a name="line.545"></a>
<span class="sourceLineNo">546</span>   *    area of the function of width == K.<a name="line.546"></a>
<span class="sourceLineNo">547</span>   *<a name="line.547"></a>
<span class="sourceLineNo">548</span>   * Let's dive into this function now:<a name="line.548"></a>
<span class="sourceLineNo">549</span>   *<a name="line.549"></a>
<span class="sourceLineNo">550</span>   * When we have storedPermits &lt;= halfPermits (the left portion of the function), then<a name="line.550"></a>
<span class="sourceLineNo">551</span>   * we spend them at the exact same rate that<a name="line.551"></a>
<span class="sourceLineNo">552</span>   * fresh permits would be generated anyway (that rate is 1/stableInterval). We size<a name="line.552"></a>
<span class="sourceLineNo">553</span>   * this area to be equal to _half_ the specified warmup period. Why we need this?<a name="line.553"></a>
<span class="sourceLineNo">554</span>   * And why half? We'll explain shortly below (after explaining the second part).<a name="line.554"></a>
<span class="sourceLineNo">555</span>   *<a name="line.555"></a>
<span class="sourceLineNo">556</span>   * Stored permits that are beyond halfPermits, are mapped to an ascending line, that goes<a name="line.556"></a>
<span class="sourceLineNo">557</span>   * from stableInterval to 3 * stableInterval. The average height for that part is<a name="line.557"></a>
<span class="sourceLineNo">558</span>   * 2 * stableInterval, and is sized appropriately to have an area _equal_ to the<a name="line.558"></a>
<span class="sourceLineNo">559</span>   * specified warmup period. Thus, by point (4) above, it takes "warmupPeriod" amount of time<a name="line.559"></a>
<span class="sourceLineNo">560</span>   * to go from maxPermits to halfPermits.<a name="line.560"></a>
<span class="sourceLineNo">561</span>   *<a name="line.561"></a>
<span class="sourceLineNo">562</span>   * BUT, by point (3) above, it only takes "warmupPeriod / 2" amount of time to return back<a name="line.562"></a>
<span class="sourceLineNo">563</span>   * to maxPermits, from halfPermits! (Because the trapezoid has double the area of the rectangle<a name="line.563"></a>
<span class="sourceLineNo">564</span>   * of height stableInterval and equivalent width). We decided that the "cooldown period"<a name="line.564"></a>
<span class="sourceLineNo">565</span>   * time should be equivalent to "warmup period", thus a fully saturated RateLimiter<a name="line.565"></a>
<span class="sourceLineNo">566</span>   * (with zero stored permits, serving only fresh ones) can go to a fully unsaturated<a name="line.566"></a>
<span class="sourceLineNo">567</span>   * (with storedPermits == maxPermits) in the same amount of time it takes for a fully<a name="line.567"></a>
<span class="sourceLineNo">568</span>   * unsaturated RateLimiter to return to the stableInterval -- which happens in halfPermits,<a name="line.568"></a>
<span class="sourceLineNo">569</span>   * since beyond that point, we use a horizontal line of "stableInterval" height, simulating<a name="line.569"></a>
<span class="sourceLineNo">570</span>   * the regular rate.<a name="line.570"></a>
<span class="sourceLineNo">571</span>   *<a name="line.571"></a>
<span class="sourceLineNo">572</span>   * Thus, we have figured all dimensions of this shape, to give all the desired<a name="line.572"></a>
<span class="sourceLineNo">573</span>   * properties:<a name="line.573"></a>
<span class="sourceLineNo">574</span>   * - the width is warmupPeriod / stableInterval, to make cooldownPeriod == warmupPeriod<a name="line.574"></a>
<span class="sourceLineNo">575</span>   * - the slope starts at the middle, and goes from stableInterval to 3*stableInterval so<a name="line.575"></a>
<span class="sourceLineNo">576</span>   *   to have halfPermits being spend in double the usual time (half the rate), while their<a name="line.576"></a>
<span class="sourceLineNo">577</span>   *   respective rate is steadily ramping up<a name="line.577"></a>
<span class="sourceLineNo">578</span>   */<a name="line.578"></a>
<span class="sourceLineNo">579</span>  private static class WarmingUp extends RateLimiter {<a name="line.579"></a>
<span class="sourceLineNo">580</span><a name="line.580"></a>
<span class="sourceLineNo">581</span>    final long warmupPeriodMicros;<a name="line.581"></a>
<span class="sourceLineNo">582</span>    /**<a name="line.582"></a>
<span class="sourceLineNo">583</span>     * The slope of the line from the stable interval (when permits == 0), to the cold interval<a name="line.583"></a>
<span class="sourceLineNo">584</span>     * (when permits == maxPermits)<a name="line.584"></a>
<span class="sourceLineNo">585</span>     */<a name="line.585"></a>
<span class="sourceLineNo">586</span>    private double slope;<a name="line.586"></a>
<span class="sourceLineNo">587</span>    private double halfPermits;<a name="line.587"></a>
<span class="sourceLineNo">588</span><a name="line.588"></a>
<span class="sourceLineNo">589</span>    WarmingUp(SleepingTicker ticker, long warmupPeriod, TimeUnit timeUnit) {<a name="line.589"></a>
<span class="sourceLineNo">590</span>      super(ticker);<a name="line.590"></a>
<span class="sourceLineNo">591</span>      this.warmupPeriodMicros = timeUnit.toMicros(warmupPeriod);<a name="line.591"></a>
<span class="sourceLineNo">592</span>    }<a name="line.592"></a>
<span class="sourceLineNo">593</span><a name="line.593"></a>
<span class="sourceLineNo">594</span>    @Override<a name="line.594"></a>
<span class="sourceLineNo">595</span>    void doSetRate(double permitsPerSecond, double stableIntervalMicros) {<a name="line.595"></a>
<span class="sourceLineNo">596</span>      double oldMaxPermits = maxPermits;<a name="line.596"></a>
<span class="sourceLineNo">597</span>      maxPermits = warmupPeriodMicros / stableIntervalMicros;<a name="line.597"></a>
<span class="sourceLineNo">598</span>      halfPermits = maxPermits / 2.0;<a name="line.598"></a>
<span class="sourceLineNo">599</span>      // Stable interval is x, cold is 3x, so on average it's 2x. Double the time -&gt; halve the rate<a name="line.599"></a>
<span class="sourceLineNo">600</span>      double coldIntervalMicros = stableIntervalMicros * 3.0;<a name="line.600"></a>
<span class="sourceLineNo">601</span>      slope = (coldIntervalMicros - stableIntervalMicros) / halfPermits;<a name="line.601"></a>
<span class="sourceLineNo">602</span>      if (oldMaxPermits == Double.POSITIVE_INFINITY) {<a name="line.602"></a>
<span class="sourceLineNo">603</span>        // if we don't special-case this, we would get storedPermits == NaN, below<a name="line.603"></a>
<span class="sourceLineNo">604</span>        storedPermits = 0.0;<a name="line.604"></a>
<span class="sourceLineNo">605</span>      } else {<a name="line.605"></a>
<span class="sourceLineNo">606</span>        storedPermits = (oldMaxPermits == 0.0)<a name="line.606"></a>
<span class="sourceLineNo">607</span>            ? maxPermits // initial state is cold<a name="line.607"></a>
<span class="sourceLineNo">608</span>            : storedPermits * maxPermits / oldMaxPermits;<a name="line.608"></a>
<span class="sourceLineNo">609</span>      }<a name="line.609"></a>
<span class="sourceLineNo">610</span>    }<a name="line.610"></a>
<span class="sourceLineNo">611</span><a name="line.611"></a>
<span class="sourceLineNo">612</span>    @Override<a name="line.612"></a>
<span class="sourceLineNo">613</span>    long storedPermitsToWaitTime(double storedPermits, double permitsToTake) {<a name="line.613"></a>
<span class="sourceLineNo">614</span>      double availablePermitsAboveHalf = storedPermits - halfPermits;<a name="line.614"></a>
<span class="sourceLineNo">615</span>      long micros = 0;<a name="line.615"></a>
<span class="sourceLineNo">616</span>      // measuring the integral on the right part of the function (the climbing line)<a name="line.616"></a>
<span class="sourceLineNo">617</span>      if (availablePermitsAboveHalf &gt; 0.0) {<a name="line.617"></a>
<span class="sourceLineNo">618</span>        double permitsAboveHalfToTake = Math.min(availablePermitsAboveHalf, permitsToTake);<a name="line.618"></a>
<span class="sourceLineNo">619</span>        micros = (long) (permitsAboveHalfToTake * (permitsToTime(availablePermitsAboveHalf)<a name="line.619"></a>
<span class="sourceLineNo">620</span>            + permitsToTime(availablePermitsAboveHalf - permitsAboveHalfToTake)) / 2.0);<a name="line.620"></a>
<span class="sourceLineNo">621</span>        permitsToTake -= permitsAboveHalfToTake;<a name="line.621"></a>
<span class="sourceLineNo">622</span>      }<a name="line.622"></a>
<span class="sourceLineNo">623</span>      // measuring the integral on the left part of the function (the horizontal line)<a name="line.623"></a>
<span class="sourceLineNo">624</span>      micros += (stableIntervalMicros * permitsToTake);<a name="line.624"></a>
<span class="sourceLineNo">625</span>      return micros;<a name="line.625"></a>
<span class="sourceLineNo">626</span>    }<a name="line.626"></a>
<span class="sourceLineNo">627</span><a name="line.627"></a>
<span class="sourceLineNo">628</span>    private double permitsToTime(double permits) {<a name="line.628"></a>
<span class="sourceLineNo">629</span>      return stableIntervalMicros + permits * slope;<a name="line.629"></a>
<span class="sourceLineNo">630</span>    }<a name="line.630"></a>
<span class="sourceLineNo">631</span>  }<a name="line.631"></a>
<span class="sourceLineNo">632</span><a name="line.632"></a>
<span class="sourceLineNo">633</span>  /**<a name="line.633"></a>
<span class="sourceLineNo">634</span>   * This implements a trivial function, where storedPermits are translated to<a name="line.634"></a>
<span class="sourceLineNo">635</span>   * zero throttling - thus, a client gets an infinite speedup for permits acquired out<a name="line.635"></a>
<span class="sourceLineNo">636</span>   * of the storedPermits pool. This is also used for the special case of the "metronome",<a name="line.636"></a>
<span class="sourceLineNo">637</span>   * where the width of the function is also zero; maxStoredPermits is zero, thus<a name="line.637"></a>
<span class="sourceLineNo">638</span>   * storedPermits and permitsToTake are always zero as well. Such a RateLimiter can<a name="line.638"></a>
<span class="sourceLineNo">639</span>   * not save permits when unused, thus all permits it serves are fresh, using the<a name="line.639"></a>
<span class="sourceLineNo">640</span>   * designated rate.<a name="line.640"></a>
<span class="sourceLineNo">641</span>   */<a name="line.641"></a>
<span class="sourceLineNo">642</span>  private static class Bursty extends RateLimiter {<a name="line.642"></a>
<span class="sourceLineNo">643</span>    Bursty(SleepingTicker ticker) {<a name="line.643"></a>
<span class="sourceLineNo">644</span>      super(ticker);<a name="line.644"></a>
<span class="sourceLineNo">645</span>    }<a name="line.645"></a>
<span class="sourceLineNo">646</span><a name="line.646"></a>
<span class="sourceLineNo">647</span>    @Override<a name="line.647"></a>
<span class="sourceLineNo">648</span>    void doSetRate(double permitsPerSecond, double stableIntervalMicros) {<a name="line.648"></a>
<span class="sourceLineNo">649</span>      double oldMaxPermits = this.maxPermits;<a name="line.649"></a>
<span class="sourceLineNo">650</span>      /*<a name="line.650"></a>
<span class="sourceLineNo">651</span>       * We allow the equivalent work of up to one second to be granted with zero waiting, if the<a name="line.651"></a>
<span class="sourceLineNo">652</span>       * rate limiter has been unused for as much. This is to avoid potentially producing tiny<a name="line.652"></a>
<span class="sourceLineNo">653</span>       * wait interval between subsequent requests for sufficiently large rates, which would<a name="line.653"></a>
<span class="sourceLineNo">654</span>       * unnecessarily overconstrain the thread scheduler.<a name="line.654"></a>
<span class="sourceLineNo">655</span>       */<a name="line.655"></a>
<span class="sourceLineNo">656</span>      maxPermits = permitsPerSecond; // one second worth of permits<a name="line.656"></a>
<span class="sourceLineNo">657</span>      storedPermits = (oldMaxPermits == 0.0)<a name="line.657"></a>
<span class="sourceLineNo">658</span>          ? 0.0 // initial state<a name="line.658"></a>
<span class="sourceLineNo">659</span>          : storedPermits * maxPermits / oldMaxPermits;<a name="line.659"></a>
<span class="sourceLineNo">660</span>    }<a name="line.660"></a>
<span class="sourceLineNo">661</span><a name="line.661"></a>
<span class="sourceLineNo">662</span>    @Override<a name="line.662"></a>
<span class="sourceLineNo">663</span>    long storedPermitsToWaitTime(double storedPermits, double permitsToTake) {<a name="line.663"></a>
<span class="sourceLineNo">664</span>      return 0L;<a name="line.664"></a>
<span class="sourceLineNo">665</span>    }<a name="line.665"></a>
<span class="sourceLineNo">666</span>  }<a name="line.666"></a>
<span class="sourceLineNo">667</span><a name="line.667"></a>
<span class="sourceLineNo">668</span>  @VisibleForTesting<a name="line.668"></a>
<span class="sourceLineNo">669</span>  static abstract class SleepingTicker extends Ticker {<a name="line.669"></a>
<span class="sourceLineNo">670</span>    abstract void sleepMicrosUninterruptibly(long micros);<a name="line.670"></a>
<span class="sourceLineNo">671</span><a name="line.671"></a>
<span class="sourceLineNo">672</span>    static final SleepingTicker SYSTEM_TICKER = new SleepingTicker() {<a name="line.672"></a>
<span class="sourceLineNo">673</span>      @Override<a name="line.673"></a>
<span class="sourceLineNo">674</span>      public long read() {<a name="line.674"></a>
<span class="sourceLineNo">675</span>        return systemTicker().read();<a name="line.675"></a>
<span class="sourceLineNo">676</span>      }<a name="line.676"></a>
<span class="sourceLineNo">677</span><a name="line.677"></a>
<span class="sourceLineNo">678</span>      @Override<a name="line.678"></a>
<span class="sourceLineNo">679</span>      public void sleepMicrosUninterruptibly(long micros) {<a name="line.679"></a>
<span class="sourceLineNo">680</span>        if (micros &gt; 0) {<a name="line.680"></a>
<span class="sourceLineNo">681</span>          Uninterruptibles.sleepUninterruptibly(micros, TimeUnit.MICROSECONDS);<a name="line.681"></a>
<span class="sourceLineNo">682</span>        }<a name="line.682"></a>
<span class="sourceLineNo">683</span>      }<a name="line.683"></a>
<span class="sourceLineNo">684</span>    };<a name="line.684"></a>
<span class="sourceLineNo">685</span>  }<a name="line.685"></a>
<span class="sourceLineNo">686</span>}<a name="line.686"></a>




























































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